Hi,
So you will want to look up the average GMAT scores at each program you are interested in (all found on their websites); for example HEC is about 715. For best chances you'd want to be near or above their average ideally. I generally recommend 2-3 months to prep for the GMAT. Deadlines vary and you'll also want to look it up for each school, but generally between Sept-Jan. If you are ready earlier, we'd recommend applying sooner if feasible. For example for HEC here are some deadline details:
https://www.hec.edu/Masters-programs/Mas ... /AdmissionOtherwise, continue to do all you can to excel at work; cultivate strong relationships for recommendations; and think and plan for your essays, so that you have a convincing story to explain why you need the degree.
In terms of it being a 'good' degree, well that is a very subjective question! Certainly it can help many in their career; I would say you do want to know exactly why you want the degree, how it will help you career-wise, and what you'll get out of it before you apply. Try to continue career research and speak with people who have the degree and/or are in the desired area you'd like to change into professionally.
Good luck!!